Initially, the Zadroga 9/11 Health and Compensation Act -- the fund established in 2010 and named for police detective James Zadroga, who died at age 34 after working at Ground Zero -- included only a short list of illnesses that qualified for compensation. Cancer was excluded because of a lack of scientific evidence linking any form of the disease to conditions in the debris pile, even though many of the 50,000 9/11 first responders believe they got cancer -- among other illnesses -- because of their exposure to dust and other substances at Ground Zero.

"We received a petition to consider adding cancer from the New York Congressional Delegation," Howard said in a statement, adding that the WTC Health Program's Scientific/Technical Advisory Committee recommended adding dozens of cancers to the coverage list in June.

The expansion will go into effect 30 days after it is published in the Federal Register.

The government says 2,976 people were killed when the terrorists hijacked passenger jets and flew them into the World Trade Center in New York City and the Pentagon in Arlington, Va. , on Sept. 11, 2001. Passengers aboard a third flight that is believed to have been destined for another Washington, D.C, target -- possibly the U.S. Capitol building or the White House -- took over the aircraft. It crashed into an open field in Shanksville, Pa.

The fire and collapse of the World Trade Center's twin towers contaminated the nearby air with particles of glass, asbestos, cement, lead, gypsum, calcium carbonate, other metal particles and other toxins.

It is believed that exposure to this dust through the lungs and skin has contributed to the asthma, gastrointestinal problems, and possibly the increased cancer risk experienced by rescue workers, especially those who were on the site immediately after the attack, when the cloud of debris dust was its thickest.

The pH of the dust was very high, meaning it was highly alkaline.

"That means it's extremely caustic and would be like inhaling powdered lye or Drano," Dr. Philip Landrigan, dean of global health at the Mount Sinai School of Medicine in New York, told ABC News in a previous interview.

Asbestos causes lung and other types of cancer, while lead and other heavy metals can be toxic to the brain.

The Zadroga Act provides first responders with screening and treatment for health problems associated with working at Ground Zero. It also created a $4.3 billion fund to compensate affected first responders for any wage or other financial losses they incurred as a result of working at Ground Zero.

About 40,000 Sept. 11 responders and survivors receive monitoring and 20,000 get treatment for their illnesses as part of the Zadroga Act's health program.

The full list of cancers included is below.

? Malignant neoplasms of the lip, tongue, salivary gland, floor of mouth, gum and other mouth, tonsil, oropharynx, hypopharynx, and other oral cavity and pharynx